A large red balloon is
rising at the rate of 20 ft/sec. The balloon is 10 ft above the ground at
the point in time that the back end of a green car is directly below the bottom
of the balloon. The car is traveling at 40 ft/sec. What is the rate
of change of the distance between the bottom of the balloon and the point on
the ground directly below the back of the car one second after the back of the
car is directly below the balloon?
